Method of making a slug tuner



June 28, 1960 F. G. MAsoN 2,942,333

METHOD op MAKING A SLUG TUNER 1 Filed April 26, 1955 l IN VEN TOR. francas Mason United States Patent O METHOD F MAKING A SLUG TUNER Francis G. Mason, Weston, Conn., assignor to Aladdin Industries, Incorporated, Nashville, Tenn., a corporation of Illinois Filed Apr. 26, 1955, Ser. No. 503,921

Claims. (Cl. 29-155.57)

One principal object of the invention is to provide a method of making a new and improved slug tuner having an extremely wide range of frequency variation, so that, for example, the tuner may be able to cover the present very high frequency (VHF) television band extending from 50 to 216 megacycles.

Another object is to provide a method of making a new and improved tuner having a coil which is supported internally within a form so that the tuning slug will move within the coil in extremely closely spaced relation thereto.

It is a further object of the invention to provide a method of making a tuner of the foregoing character in which the movable tuning slug is received in a bore which cuts into the turns of the tuning coil so that the slug will have a maximum elect on the inductance of the coil.

Further objects and advantages of the invention will appear from the following description, taken with the accompanying drawings, in which:

Figure 1 is a somewhat diagrammatic longitudinal cross section view of an exemplary slug-type tuner constituting an illustrative embodiment of the invention.

Fig. 2 is an exploded sectional view of a holder and a coil employed in making the tuner of Fig. l.

Fig. 3 is an end view of the holder of Fig. 2.

Fig. 4 is an end view of the coil of Fig. 2.

Fig. 5 is a longitudinal sectional view showing the holder and the coil after the coil has been imbedded in a plastic material received within the holder, the view also illustrating the manner of drilling out the plastic material.

Fig. 6 is a longitudinal sectional view of the finished coil imbedded in plastic within the holder, the view being similar to Fig. 1 but with the core or tuning slug removed from the coil.

Fig. 7 is a cross-sectional view taken generally along a line 7-7 in Fig. 6.

If the drawings are considered in greater detail, it will be seen that Fig. l illustrates a slug-type tuner 11, comprising a tuning slug 12 which is movable within a coil 13. It will be seen that the coil 13 is supported internally within a tubular holder 14 made of any suitable insulating material, such as a hard, substantially rigid, synthetic resinous plastic material. Formed within the holder 14 are first and second coaxially aligned bores or cylindrical openings 15 and 16, the bore 15 being smaller in diameter than the bore 16. In other words, the bore 15 may be considered to be a reduced end portion of the bore 16.

The coil 13 is helical in form and is made with a plurality of turns, composed of any suitable conductive metal strand, such as the illustrated wire, which is of generally circular cross section. The coil is imbeddedin a bushing-like or sleeve-like element 17 of electrically rice insulating, resinous plastic material. It will be seen that the plastic imbedding material 17 is received within the bore 16 so as to secure the coil 13 in place within the holder 14.

The coil 13 is formed with a pair of end leads 18 and 19 and an intermediate tap or lead 20 connected to an intermediate point along the length of the coil. A slot 21 is formed longitudinally in the holder 14 so that the leads 18-20 may be brought radially outwardly from the bore 16. As shown, the slot 21 extends along the entire length of the large bore 16, but not along the smaller bore 15. The plastic imbedding material 17 lls all portions of the slot 21 not occupied by the coil 13.

Within the plastic imbedding material 17, a bore or cylindrical opening 22 is formed, so as to constitute a smooth continuation of the bore 15. In other words, the bores 15 and 22 are coaxially aligned and are of the same diameter. It will be seen that the bore 22 cuts into the turns of the coil 13. ln other words, the inside of the coil is formed with an internal cylindrical surface element 23 which extends helically along the turns of the coil. As shown to best advantage in Fig. 6, the cylindrical surface element 23 is flush with the imbedding plastic material 17 along with bore 22.

It will be seen that the tuning core 12 is received with a close sliding fit within the bores 15 and 22. In this way, the core 12 is movable within the bore 22 in closely spaced relation to the cylindrical surface element 23 of the coil 13. Accordingly, the core has a maximum eti'ect upon the inductance of the coil 13.

It will be seen that the illustrated core or slug 12 is formed in two coaxially aligned cylindrical portions 24 and 25 arranged end to end. The lefthand portion 24 may be made of any suitable conductive metal, such as silver, copper, aluminum or brass, for example. yOn the other hand, the righthand portion 25 of the tuning slug `12 is preferablymade of a low-loss, electrically insulating magnetic material, such as sintered iron ferrite. Such ferrite and other low-loss magnetic materials are well known in the art. Slugs of such materials are usually made by molding the material in finely-powdered form, with a suitable binder, into the desired shape, and then sintering the material.

In order to insulate the core 12 from the coil 13, the core 12 is provided with a thin insulating coating 26 made of a suitable low-loss insulating material, such as various synthetic plastic lacquer-like materials. The material of the coating 26 should also be hard and smooth so as to resist mechanical wear. A number of such coating materials are available commercially. The insulating layer 26 need be only about .001" in thickness. A minimum thickness is desirable to obtain the widest possible tuning range.

It will be seen that the core 12 is received within the bores 15 and 22 with a close sliding t. The fit is made as close as possible so that the core 12 will be spaced a minimum distance from the coil 13 as it moves through the bore 22. It is preferable that the spacing between the outer surface of the core and the inner cylindrical surface element 23 of the coil 13 be no more than .003.

Any suitable mechanism may be provided for moving the core 12 within the coil 13. i In this case, such movement is effected by means of a cam 27 mounted on a rotatable shaft 28. The cam is engaged by a balltype roller 29 mounted in a member 30 which is fixed to the lefthand end of the core 12. A wire spring 31 is received in a slot 32 to bias the core 12 to the left and thereby maintain the roller 29 in engagement with the cam 27.

In making the tuner 11, the coil 13 is wound on a tions, forming an electrically insulating holder with an opening therein of a size to receive said coil, forming laterally extending terminal leads on said coil, forming said holder with a longitudinal slot extending radially from said opening for receiving said leads, inserting said coil into said opening in said holder with said leads extending outwardly therefrom through said slot, filling said opening with an electrically insulating liquid hardenable resinous plastic material and thereby imbedding said coil in said material, said plastic material being capable of bonding with said coil and said holder, hardening said material to bond said material to said coil `and said holder while maintaining said convolutions in spaced relation, cutting a bore through said material and said coil of a diameter to cut into said convolutions of said coil and thereby form cylindrical surface elements therein, said bore being cut substantially cylindrical and with said bore comprising said cylindrical inner surface elements of said spaced convolutions, said plastic material rigidly supporting said coil during said cutting operation, and forming an electrically insulating tuning core of a diameter to be slideably received in said last-mentioned bore, said core being formed with an insulating coating thereon to insulate said core from said wire.

4, In a method of making a tuner, the steps comprising forming an electrically insulating tubular holder with first fand second coaxially aligned interconnected bores therein, said first bore being substantially smaller in diameter than said second bore, winding conductive metal wire on a cylindrical form and thereby forming a generally helical coil having a plurality of spaced convolutions, removing said coil from said form, positioning said coil in said second bore, said second bore corresponding in diameter to the outer diameter of said coil, lling said second bore with an electrically insulating liquid hardenable plastic material and thereby imbedding said coil therein, said plastic material being capable of bonding with said coil and said holder, hardening said material to bond said material to said coil and said holder while maintaining said convolutions in spaced relation, and drilling out said plastic material from the inside of said coil along the entire length thereof to form a cylindrical opening extending through said plastic material as a smooth continuation of said iirst bore, said drilling being done to a greater diameter than the inner diameter of said coil so that said drilling will cut into said convolutions of said coil and will form cylindrical inner surface elements on said convolutions flush with said plastic material in said drilling opening, said plastic material supporting said coil in rigid relation to said holder during said drilling operation, said drilling operation producing a substantially uniform internal cylindrical surface within and along the entire length of said coil, with said cylindrical surface comprising said inner surface elements on said spaced convolutions.

5. In a method of making a tuner, the steps comprising forming an electrically insulating tubular holder with iirst and second coaxially aligned interconnected bores therein, said first bore being substantially smaller in diameter than said second bore, forming a longitudinal slot in said holder and extending outwardly from said second bore, winding conductive metal wire on a cylindrical form and thereby forming a generally helical coil having a plurality of spaced convolutions, removing said coil from said form, forming radial terminal leads on said coil, positioning said coil in said second bore with said radial leads extending outwardly through said slot, said bore corresponding in diameter to the outer diameter of said coil, lling said second bore and said slot with an electrically insulating liquid hardenable plastic material and thereby imbedding said coil therein, said plastic material being capable of bonding with said coil and said holder, hardening said material to bond said material to said coil and said holder while maintaining said convolutions in spaced relation, drilling out said plastic material from the inside of said coil along the entire length thereof to form a cylindrical opening extending through said plastic material as a smooth continuation of said rst bore, said drilling being done to a greater diameter than the inner diameter of said coil so that said drilling will cut into said convolutions of said coil and will form cylindrical inner surface elements on said convolutions flush with said plastic material in said drilled opening, said plastic material supporting said coil in rigid relation to said holder during said drilling operation, said drilling operation producing a substantially uniform internal cylindrical surface within and along the entire length of said coil, with said cylindrical surface comprising said inner surface elements on said spaced convolutions, forming a tuning core with one end portion of electrically insulating magnetic material and an opposite end portion of electrically conductive material, applying an insulating coating to said core to insulate said core from said coil, and slideably disposing said core in said first bore and said drilled opening, said core being formed of a diameter to make a close sliding iit with said drilled opening.

References Cited in the iile of this patent UNITED STATES PATENTS 2,404,185 Mann Iuly 16, 1946 2,455,355 Combs Dec. 7,.1948 2,459,605 Warnken Ian. 18, 1949 2,552,999 Pannell May 15, 1951 2,568,310 Whitten Sept. 18, 1951 2,652,623 Marden Sept. 22, 1953 FOREIGN PATENTS 551,139 Great Britain Feb. 9, 1943 140,866 Australia Apr. 18, 1951 

